Air-heating system



m 1947. H. B. HOLTHOUSE 2,427,673

AIR HEATING SYSTEM Filed May 15, 1942 4 Sheets-Sheet 1 I J x i 4 6 I 47five/2%]? Sept 1947. H. a. HOLTHOUSE 2,427,673

AIR HEATING SYSTEM Filed May 15, 1942 4 Sheets-Sheet 2 Sept. 23, 1947.H. B. HoL'n-lousE 2,427,673

AIR HEATING SYSTEM Filed May 15, 1942 4 Sheets-Sheet 3 f f /r flaiify p1947- H. B. HOLTHOUSE 2,427,673

AIR HEATING SYSTEM Filed May 15, 1942 4 Sheets-Sheet 4 Patented Sept.23, 1947 UNITED STATES AIR-HEATING SYSTEM Harry B. Holthouse, Chicago,11]., assignor to Motorola, Inc., a corporation of Illinois ApplicationMay 15, 1942, Serial No. 443,126

Claims. (Cl. 237-2) This invention relates generally to air heatingsystems and in particular to a system for heatin and distributing air inan aircraft. I In large aircrafts and particularly in large bombingplanes having a plurality of operators located in different parts of thefuselage, such as the nose, tail and body portions, many diflicultieshave been encountered in comfortably heating the portions occupied bythe operators. It is recognized of course that planes of bomber typeoperate at extreme high altitudes and corresponding extreme coldtemperatures and have cruising speeds normally of several hundred milesper hour. In a heating system having a single heated air outlet thedistribution of heat to all portions or spaces to be heated is preventedby any drafts or air currents passing through the plane. Because of thespeeds at which these bomber planes travel it is readily understandablethat any small openings in the fuselage to the atmosphere result in highvelocity and turbulent air drafts within the plane. Heated air, whendischarged from a single source may, therefore, be carried entirelyoutside of the plane without ever passing through some portions thereof.In attempts to overcome these disadvantages in the air systems havingbut a single heat outlet, air from such outlet has been piped to theplurality of spaces or compartments to be heated. This procedure,however, is generally unsatisfactory because of the bulk of the hot airconduits, the inconvenience in their assembly, and further because ofthe heat lost in the transmission of the heated air.

In further efforts to provide a suitable heating system for an aircrafthaving a plurality of spaces therein, a heating unit of internalcombustion type corresponding to each space is provided, with the airand fuel mixture for burning in the heating units being supplied from acommon mixing unit such as a carburetor. This system is not entirelysuccessful, however, because in the transmission of the air and fuelmixture the fuel condenses from the mixture so that the operation of theheating units is relatively ineflicient and unreliable.

It is an object of this invention, therefore, to provide an improved airheating and distributing system.

.Another object is to provide an improved air heating and distributingsystem for an aircraft having spaces or stations to be heated locatedremotely from each other.

A further object of this invention is to provide a heating system for anaircraft comprised of a plurality of heating units of internalcombustion type each of which is adapted to be operated over a widerange of altitudes of varying pressures and oxygen densities.

Yet a further object of this invention is to pro- 2 vide an air heatingsystem which utilizes a plurality of combustion portions having air andfuel separately fed thereto for burning from common air and fuel supplymeans.

Yet another object of this invention is to Provide an air heating systemhaving a plurality of heat distributing portions located remotely fromeach other and operatively associated so as to completely eliminat anyheat transmission losses therebetween.

Still another object is to provide a, heating system having a heatingunit of internal combustion type in each one of a plurality of stationsin which a proper air and fuel mixture is pre pared at each station andretained until ready for burning.

A feature of this invention is found in the provision of an air heatingsystem comprised of a plurality of combustion portions for heating airadapted to be operated at a low pressure, with air and fuel beingseparately conducted to a corresponding portion at a pressure above suchlow pressure. Each combustion portion is operatively associated withmeans adapted to reduce the air and fuel supply pressures tosubstantially said low pressure and to mix the same for burning at suchlow pressure. The conduits for carrying the air and fuel to thecombustion portions can thus be relatively small while a combustionportion can be located wherever heat is desired.

Another feature of this invention is found in the provision of an airheating system for an aircraft comprised of a plurality of spacedcombustion portions operated at substantially atmosheric pressure andfed from common air and fuel supply means, in which the air and fuel areseparately supplied to each combustion portion in relative quantitiesproviding for a substantial- 1y uniform mixture over a wide range ofaltitudes of varying oxygen contents and pressures.

The air and fuel are supplied at atmospheric temperature so that theproblem of heat losses in the air and fuel supply systems is entirelyeliminated.

Further objects, features, and advantages of this invention will becomeapparent from the following description when taken in connection withthe accompanying drawings in which:

Fig. 1 is a diagrammatic illustration of the fuselage of a bombing planeshowing the arrangement therein of the operators compartments which areto be heated Fig. 2 illustrates diagrammatically the operating'arrangement of a plurality of heating units comprising the heatingsystem of this invention;

Fig. 3 is a sectional detail view of a heating unit;

Fig. 4 is a transverse sectional view through the combustion portion ofa heating unit taken along the line 4-4 in Fig. 3;

Fig. 5 is a detail sectional view of an air and fuel mixing meansoperatively associated with each heating unit;

Fig. 6 is a diagrammatic control circuit for opcrating the heatingsystem shown in Fig. 2;

Fig. 7 is a sectional view of a modified form of heating unit with partsthereof broken away to more clearly show the construction thereof;

Fig. 8 is a transverse sectional view taken along the line 8--8 in Fig,'7;

Fig, 9 shows the application of a heating unit in conjunction with aninflatable garment adapted to be worn by an operator of an aircraft;

Fig 10 is a detail transverse sectional view of a fuel metering meandiagrammatically illustrated in Fig. 2 for each heating unit;

Fig. 11 is an enlarged fragmentary elevational view as seen along theline illl in Fig. 2; and

Fig. 12 is a detail plan view of a combination fuel valve and switchunit utilized for each heating unit and diagrammatically illustrated inFigs. 2 and 6. t In the practice of this invention there is provided anair heating and distributing system for an aircraft having a pluralityof operator compartments therein, which comprises a heating unit ofinternal combustion type located in each of such compartments. Eachheating unit includes a combustion portion having a corresponding fuelconditioning means for preparing an air and fuel mixture for burningtherein. Air and fuel are supplied separately to each fuel conditioningmeans from a common supply means, with such air and fuel being heatedtogether to at least a fuel vaporizing temperature by electric heatingmeans corresponding to each conditioning means. The separate feeding ofair and fuel to each heating unit and the preparation of the air andfuel mixture for burning immediately at a corresponding combustionportion assures a proper mixture for burning and resultant efficientoperation of each heating unit. Electric air moving means correspondingto each combustion portion projects air to be heated in a heat exchangerelation with a combustion portion and into a corresponding compartment.The electric air moving means and heating means corresponding toa-combustion portion are connected together in a common circuit having aplug element adapted for connection with a source of electrical powersuch as a power circuit in the aircraft. By virtue of thisconstructionand assembly of the combustion portions the air in eachcompartment is positively heated while the bulk and complexity of the 1means common to such portions and extended between the same are of a'small size to provide for their installation in a minimum of space.

At high altitudes the operation of internal combustion devices isgreatly affected by the variations in barometric pressures and oxygensupply. Thusat high-altitudes and a corresponding reduced ox ygencontent of the air at suchaltitude, more air must be supplied at thehigh altitudes as compared to a lower altitude or ground level toprovide for an efficient operation of the heating'unit at all altitudes.The'=invention, therefore, contemplates the provision of pressureresponsive nose and intermediate portions thereof. As showndiagrammatically in Fig, 2 the heating system is comprised of aplurality of heating units [2 of internal combustion type, only one ofwhich is indicated, corresponding in number to the compartments ll. Airfor combustion is supplied by a fan l3 from a transmission duct I4common to all of the heating units and having a connection Itcorresponding to each thereof. Fuel for each unii is supplied by a pumpi1 through a common line [8 having a branch line l9 connected to acorresponding heating unit. The pump is operatively associated throughsuitable mechanism 22 with a motor 2| of series wound type, which alsooperates the fan l3. Since each heating unit i2 is similar inconstruction and operation only one thereof will be referred to in thefollowing detailed description.

A heating unit I2 (Figs. 3 and 4) includes a housing 23 of cylindricalshape open at the opposite ends thereof. Axially extended within thehousing is a combustion portion or chamber 24 having an air supplychamber 26 at the inner end thereof which is separated from thecombustion chamber by a partition or dividing wall 21 which closes suchinner end of the combustion chamber. The outer end of the combustionchamber extends to the end 45 of the housing 23 and is closed by a coverplate 28.

The combustion chamber 24 is divided longitudinally thereof into fouraxially extending but connected passages 290-2 9d by a partition member3i of substantially X-shape. The combustion chamber inlet 32 and outlet33 are formed in the wall portion 21 in communication with the passages29a and 29d, respectively. Located within the inlet 32 is an air andfuel mixing unit. indicated generally as 34, which extends within theair supply chamber 26. The outlet 33 is provided with a tail pipe 36projected within the air supply chamber 26. Also extended within the airsupply chamber 26 is a second tail pipe 31 larger in diameter than thetail pipe 36 but in coaxial alignment therewith so as to form a spacebetween such two ail pipes within the air supply chamber 26 for apurpose to be later noted. The tail pipe 31 projects outwardly from thehousing 23 and is adapted for connection with a suitable exhaust pipe(not shown) to carry the exhaust gases away from the heating unit l2 andoutside of theaircraft.

The outer wall or body portion of the combustion chamber 24 is providedwith angularly spaced axially extending heat radiating fins 38.

Oninsertion of the combustion chamber 24 within the housing 23 the outerends of the fins 38 engage the inner periphery of the housin 23 so thatan annular passage 39 for air to be heated is formed about thecombustion chamber and within the housing. Theair to be heated 5housing-end 4.6.. The heated air is discharged from the housing 23"atthe end .45 thereof.

The air supply chamber 26 is connected directly with acorrespondingconnection IE to the commonair duct I4. In one embodimentof the invention the chamber 26 has a volume of about fifty-four cubicinches with the air therein having a pressure of less than 3 inches ofwater.

small volume of the chamber 26 the air duct i4 is correspondinglysmall-so that it can be in- 2 the duct l4 may be progressively decreasedin.

its cross sectional area between the first and last heating units I!connected thereto to provide for a suflicient volume of air beingsupplied to all of such units. The proper distribution of supply air tothe heating units I! may be further facilitated by the operation of avalve member 58 arranged within a corresponding air duct |6 to controlthe flow of air therethrough.

A corresponding fuel line I!) for the heating unit I! is connected atone end to the common fuel line I8 and at its opposite end to a fuelinjection nozzle 41 formed as a part of the air and fuel mixing means34. The rate of feed or supply of fuel to the mixing means 34 isdetermined by a fuel feed unit 63 connected inthe fuel line connectionl9. This unit 63 is diagrammatically illustrated in Fig. 2 and shown indetail in Fig lil and includes a body member 64 of sleeve formthreadablyconnected at its inlet end 61 directly with the fuel line 19,and at its outlet end to a bored plug 66 which in turn is connected tothe line I911. The body member 64 is of a length to provide for theformation therein between its end 61 and the plug 66 of a cavity or fuelreservoir 68 which is filled with a fuel filter of felt or othersuitable like material. The reservoir 68 is in fluid connection with abellows unit 69 comprised of a pair of flexible mating diaphragms havingan air space or pocket therebetween. The expansion and contraction ofthe bellows unit 69 is responsive to the fluid pressures within thereservoir 68 and serves to cushion or absorb any fuel surges in thecavity in a well known manner, so as to provide for a substantiallyuniform pressure and flow of the fuel at the reservoir outlet. Referringto Fig. it is seen that the bellows or expansible means 68 is expandedagainst the pressure of the air to the outside thereof. It is apparentof course that in high altitude flying the air pressure is reduced so asto correspond-, ingly decrease the air pressure tending to compress thebellows means. This condition impairs the function of the bellows meansto level the pulsations in the fuel resulting from the action of thepump I 1. Also at reduced air pressures the diaphragms may be entirelypulled apart by the fuel pressures pushing outwardly thereon. To assurea proper operation of the bellows means 69 at all altitudes there isprovided a casing or enclosure 10 which is air sealed about the bellowsmeans 69. The space within the casing 10 is at an atmospheric pressurecorresponding to ground level. A substantially constant air pressure isthus maintained on the bellows means 69 regardless of the flightcondition of the aircraft. It is apparent of course that any desired airpressure may be used within the casing 18 depending upon the operatingcharacteristics of the bellows means 69.

The fuel line l9a, between the unit 63 and the fuel nozzle 41 is of alength of about 9 inches. Extended over approximately two thirds of thislength and within the line I9 is a core member 1| which may be providedin wool, yarn, glass, wire or the like. The member 1| functions toretard and meter the fuel admitted to the fuel injection nozzle 41 byvirtue of its increasing the resistance to the flow of the fuel in theline I9; The flow at the core member occurs as a result of a capillaryor surface tension action between the surfaces of the core member andthe fuel line. This action provides for a definite creeping of the fuelabout the core member irrespective of the fuel pressure producing thefuel flow, an increase in pressure serving merely to accelerate thiscreeping action. Since the bellows means 68 operates to level the fuelpulsations leaving the reservoir 68 a substantially uniform fuelpressure occurs at the outlet therefor so that the fuel passes about thecore member at a substantially constant rate. Increasing the diameter ofthe core member decreases the flow through the line, but also increasesthe capillary flow of the fuel by virtue of the increase in the surfaceof the core member. It is thus readily apparent that a variation in boththe diameter and the length of the core member 1| relative to the fuelline |9a effects a corresponding variation in the metering of the fuelto the fuel injection nozzle of the conditioning means 34. Asillustrated in Fig. 2 fuel is supplied to the common fuel line It by apump l1. However it is to be understood that the fuel line I8 may beconnected directly into the fuel system of the motive power for theaircraft regardless of the operating pressure of such fuel system, sincethe proper rate of fuel feed to the conditioning means 34 can be readilyaccomplished by a proper relative selection of a'core member 1| and fuelline IS.

The air and fuel mixing means 34 (Figs. 3 and 5) includes a casingmember 48 which is closed at one end and open at the end 49 thereof withthe passage 29a. A mixing chamber 5| at the closedend of the casing 48is separated from an equalizing chamber 52 by a perforated plate member53. The equalizing chamber 52 in turn is both defined and separated fromthe combustion chamber passage No by a perforated heat insulating plate54 spaced inwardly from the open end 49 of the casing 48. Extendedsubstantially axially through the casing 48 and supported in thepartition plates 53 and 54 and projected outwardly from the closed endof the casing 46 is a combination electric heating and igniting unit 56which includes a resistance coil 51 supported in a spaced relationwithin a metal tube 58.

In the operation of the air and fuel mixing means 34 the fuel deliveredto the nozzle 41 is directed into the mixing chamber 5|, the fuel nozzlebeing located within the air supply chamber 26 and mounted directly onthe casing 48 at the mixing chamber 5|. A portion of the air for mixingwith the fuel enters the nozzle 41 from the air chamber 26 through ports59 in the fuel nozzle and travels with this fuel into the mixing chamber5|. Additional air from the air chamber 26 is admitted directly into themixing chamber 5| through apertures 6| formed in the casing 48 about thefuel injection nozzle 41. The fuel within the mixing chamber 5| isheated to at least a fuel vaporizing temperature by the combination unit56 to provide a thorough mixing thereof with the air in the mixingchamber 5|. The casing 48,'partition plate 53 and tube 58 areconstructed of a heat conducting material so as to readily receive andconduct the heat radiated by the resistance coil 51 to substantially allportions of the conditioning unit 34. The vaporous air and fuel mixturepasses through the perforated plate 53 into the equalizing chamber 52which in cooperation with the perforated insulating plate 54 acts toreduce the turbulence in the mixture and to disperse the mixturesubstantially uniformly over the entire cross section of the casing 48.This combustible mixture passes through the apertured plate 54 andacross the open end 62 of the tube 58 into the effective igniting zoneof the combination unit 53 which functions as a heat gun. In other wordsthe heat developed by the coil 51 is projected outwardly from the openend 62 of the tube 58, the heat generated being dependent upon the wattinput to the resistance coil 51. The combustible mixture is thus ignitedby virtue of the temperature at the end 62 of the tube 58 being of adegree capable of igniting such fuel without the mixture itself directlycontacting the coil 51.

As predously mentioned the air within the chamber 26 is at a pressure ofless than about 3 inches 01 water. Since the air is admitted into thecombustion chamber 24 at this pressure it is apparent that combustiontakes place within the combusti n chamber at substantially atmosphericpressure. The arrangement of the tail pipes 36 and 31 within the airchamber 26 provides for a flow of air from the chamber into the tailpipe31. This flow of air creates a Venturi action across the tail pipe 36and hence at the combustion chamber outlet 33 to facilitate the passageof the exhaust gases therefrom. The air within the chamber 26 thus actsat both the inlet 32 and outlet 33 to move the combustible mixture andexhaust gases through the combustion chamber. As is best illustrated inFig. 3 it is seen that the air supply chamber 26 also func tions as anexpansion chamber relative to the air admitted thereto from the pipe l6.As a result air may be carried in the transmission duct M at a pressureabove the pressure within the air supply chamber 26, with the pressureof the air in the duct I4 being reduced in the chamber 28 to a pressureof less than 3 inches of water because of such expansion. The duct lineH may thus be further reduced in size to provide for its installationwith a minimum of interference with the other installations in theaircraft. It is to be understood that because of the expansion functionof chamber 26 any type fan or even an air compressor could be used inplace of 'the sirocco type fan illustrated.

From the above description, therefore, it is seen that air and fuel aresupplied separately and in controlled quantities to each heating unit I2and are mixed together for burning by an air and fuel mixing means 34corresponding to each of the units. Further the air and fuel can beconducted to the heatin units under wide variations in pressure, sincethe air chamber 26 and fuel metering device 63, operatively associatedwith each of the heating units, function to reduce the air and fuelpressures to a value providing for their burning in the combustionchamber at a normal operating pressure. In connection with the air ductl4 it is obvious that such a line may be of a rigid or a flexibleconstruction since it carries only atmospheric air. In other words thereis noproblem of lost heat in the transmission of the supply air sincethe air is supplied at atmospheric temperature and is not mixed with thefuel until it reaches a fuel conditioning unit 34. As a result both theair and the fuel supply lines may be made relatively small and withoutany special heat insulating provisions.

In the control circuit for the heating system shown in Fig. 6 the motor42 and resistance coil 51 corresponding to a heating unit I 2 areconnected together in a series circuit. Each series circuit is providedwith a plug portion '|2 for connection with a corresponding electricreceptacle I3 which are connected together in series and included in apower circuit C having a battery 14. The motor 2| for the air supply fanl3 and pump I1 is connected to the power circuit through a suitable plugand socket connection 16, and in series with a voltage regulator 96 tobe later fully xplained. The operation of the motor 2| is controlled bya switch 11. Since an entire heating unit weighs about 13 pounds it iscapable of bein readily installed and removed as a complete packageunit.

Each heating unit I2 is selectively operated by a combination fuel valveand control switch unit 18 shown diagrammatically in Figs. 2 and 6 andin detail in Fig-12. The unit 18 is connected in a corresponding fuelline l9 and includes a valve member I9 having a stem portion 8| and anoperating lever or handle 82. The stem 8| has a pin 83 projectingradially therefrom, which acts as an actuator for a switch 84. When thehandle 82 is in an on position, as shown in Fig. 12, the valve member 19is in an open position and the pin 83 in a position to close the switch84. The on position thus provides for the operation of a heating unit.To stop heater operation the handle is moved to its off position. Thismanipulation closes the supply of fuel to the heater and moves the pin83 out of engagement with the switch 84 to open the same.

As was previously mentioned the motor 2| is of series Wound type so thatit inherently seeks a speed at which it will operate at full load. Inother words the motor operates to retain a constant load thereonregardless of the speed of its operation. When the heater is operated ataltitudes approaching 20,000 feet the speeding up of the motor 2|,resulting from the reduced air load on the fan by the decreased densityof the air at such altitudes, is sufiicient to compensate for thereduced air density so that a substantially constant supply of oxygen isfed through the fan inlet 86 into the duct l4 and hence to theconditioning units 34 (Figs. 2 and 11). Combustion conditions in eachheater are thus retained substantially the same as the combustionconditions at ground level. This increase in speed, however, is notgreat enough to maintain ground level combustion conditions at altitudesin excess of about 20,000 feet. In order, therefore, to maintain groundlevel heater operation at altitudes above 20,000 feet and up to about50,000 feet further compensation for the increased rarification in theair and reduction in oxygen content is provided by means now to bedescribed.

The inlet 86 to the air duct I4 is operatively associated with dampermeans 81 for controlling the passage of air therethrough to the heaterunits l2 (Figs. 2 and 11). The damper means is illustrated as bein of ausual type including louvers 88 connected to a common actuating member89 for simultaneous movement to open and closed positions relative tothe inlet 86. The actuating member 89 is operated by a bellows unit 9|which is responsive to variations in atmospheric pressures to operatethe louvers.

The bellows unit 9| is comprised of mating diaphragms 92 composed of aflexible metal or like material to form a closed space having a spring93 therein acting to push the diaphragms apart. The space within thediaphragms 92 is evacuated to a pressure of substantially zero poundsper square inch while the pressure of the spring 93 is such that atground level the atmospheric pressure is sufficient to press or squeezethe diaphragms to a closed or fully compressed position. It is readilyapparent, of course, that a closed position of the bellows does notindicate a closed position of the damper means since the louvers 8B areretained partially open at ground level to admit suficient air into theduct l4 to maintain proper combustion in the heater units i2. Furtherthe spring 93 may be calibrated so that the bellows unit 9| remainsclosed up to an altitude at which a control of the damper means isdesired. This is accomplished by setting the spring pressure tocorrespond to the pressure at the desired altitude. The bellows unit 9|is carried on a bracket 95 in a manner such that the movement of thediaphragms 92 is additive relative to the actuating bar 89. In otherwords the movement of the bar is double the movement of each diaphragm92.

To efiiciently operate the heater at all altitudes the power availablefor the operation of the motor 2|, the capacity or size of the fan l3,and the size of the inlet 86 when the louvers 88 are in full openposition are relatively determined to provide for a supply of air havingenough oxygen therein for proper combustion at the highest altitude atwhich the heaters are to operate. When this relation is determined theopening 86 and the power supplied to the motor 2| are relatively andprogressively decreased to provide for the eiiicient operation of theheaters at ground level. Since the louvers are intended to be wide openonly at the extreme altitude of 50,000 feet and corresponding rarifiedatmosphere, a partially closed position of the louvers at ground leveland corresponding heavier atmosphere permits the delivery of an oxygensupply to the heaters which is substantially equal to the supply ofoxygen at the high altitude. In the operation of the heaters, therefore,as the atmospheric pressure is reduced with an increase in altitude thebellows unit 9| is expanded by the action of the spring 93 toprogressively move the louvers 88 to a wide open position. Thisprogressive change in the size of the inlet opening 86 as varied by thelouvers 88 continues until the louvers are in their wide open positioncorresponding to the highest altitude at which the heater is adapted tooperate with ground level eificiency. As a result of the air becomingless dense with an increase in altitude the load on the motor producedby the fan decreases so that the motor increases in speed concurrentlywith the movement of the louvers to their open position. The increase inthe speed of operation of the motor 2| and hence of the fan l3 over theentire range of altitudes at which the heater is to operate isaccomplished by means now to be described.

As previously mentioned the size of the fan l3, the power applied on themotor 2| and the size of the opening 86 are relatively determined tocompensate for the reduced oxygen content of the rarified atmospheres athigh altitudes. The size of the fan l3 relative to the motor 2| is suchthat at ground level the motor is substantially incapable of operatingthe fan when the louvers 88 are in a wide open position. In other wordsthe fan is oversize relative to the motor for operation at ground levelwith the louvers 88 entirely open. The louvers 88, therefore, are onlypartially open at ground level to permit an operation of the fan l3 bythe motor 2| which provides sumcient air for combustion. However, withan increase in altitude and a resultant decrease in the air load on thefan l3 the louvers 88 may be progressively opened without stalling themotor 2|.

In the operation of a series wound motor, the increase in speed thereofis directly proportional to the reduction in the load thereon up to alimit which might be termed a fiat point or "point of constant speed.-In other words the ratio of speed to load follows a straight line curveup to a flattening out point thereon at which the speed remainssubstantially constant. This increase in the speed of a series motorwith a reduction in load is often referred to as the unwinding of themotor, The unwinding characteristic of a series type motor is utilizedin the present invention to provide for a substantially continuousincrease in the speed of operation of the motor 2| over the entire rangeof altitudes at which the heaters are to operate.

Thus referring to Fig. 11 the voltage regulator 96, previously referredto, is carried on the duct l4 and includes a regulating arm 91operatively connected to the actuating member 89 for operation by thebellows unit 9|. The voltage regulator or rheostat 96 functions toincrease the power applied to the series wound motor 2| with an increasein altitude to augment the speeding up of the motor resulting from itsbeing of series wound type. Thus for example assume the volt ageregulator at ground level to be adjusted such that the voltage appliedon the motor 2| is only about 60% of its rated voltage. With an increasein the altitude and corresponding decrease of the air load on the fan|3,' the motor 2| while operating at 60% of itsrated voltage will unrated voltage so that a third unwinding there-- of occurs. It is seen,therefore, that the series motor 2| operates to continuously increase inspeed with a reduction in load thereon for each voltage at which it isoperated. Thus by varying the applied voltage from some value below itsrated voltage to a value above its rated voltage a continuous increasein speed thereof over a wide speed range can be obtained. This operationof themotor 2| in conjunction with the use of an oversized fan andadjustable louvers 88 provides for a wide compensation for the reductionin oxygen content in the rarified atmospheres at high altitudes so thatthe supply of oxygen at all altitudes is maintained substantiallyconstant. Combustion conditions over the entire range of altitudes atwhich the heaters are operated are thus retained substantially uniform.It is to be understood of course that in those instances where a serieswound motor is not utilized that the rheostat control of this inventionmay be used to progressively increase the speed of operation of someother type motor.

Since the speed of the motor 2| as controlled by the voltage regulator96 might not be required until after some predetermined altitude, theoperation of the voltage regulator may be delayed until suchpredetermined altitude is reached. Thus the regulating arm 91 (Fig. 11)is mounted for pivotal movement on a shaft 98 which also carries an arm99 having a slot |0| therein for receiving a pin I02 mounted on a linkI03 carried on the actuating bar 89. It is seen, therefore, that the arm91 remainsstationary until the lost motion in the pin and slotconnection is taken up after a predetermined movement of the actuatingarm 89 by the bellows unit 9 I.

In conjunction with the oxygen control it may be found necessary undersome conditions of operation to change the rate of fuel feed supplied tothe heaters I 2. To maintain a substantially uniform fuel mixture at allaltitudes the rate of fuel supply may be varied concurrently with thevariation in the oxygen supply over a portion of the range of altitudesat which the heater is to operate. Thus referring to Fig. 2 the actuatorbar 49 is formed with a slot I04 adapted to receive a. pin III carriedat one end of a pivoted link member II". The opposite end of the linkmember ID! is pivotally connected with a valve member I08 formed as apart of a valve unit I 09 connected in the fuel supply line I8 ahead ofthe pipe connections I 9. The pin and slot connection I04- I06 providesfor a lost motion between the bar 89 and the link I01 so that movementof the link I! is not immediately responsive to the expansion of thebellows unit 9|. In other words, the supply of fuel to the heaters I2 isnot varied in response to atmospheric conditions until an altitude isreached at which the pin I06 is in driven engagement with the bar 89.After this engagement takes place the air and fuel supplied to thecombustion chamber is concurrently varied in response to the barometricpressures acting on the bellows unit 9|. It is to be understood, ofcourse, that under some conditions of operation the fuel may be variedover the complete range of altitudes at which the heater is to operate.

A modified form of heating unit I2 is shown in Figs. '7 and 8 which issimilar in all respects to the heating unit I2 in Fig. 3 except that theheat radiating fins 38' thereof are positioned transversely about thecombustion chamber 24'. Similar numerals of reference, therefore, willbe used to designate like parts. The combustion chamber 24' ispositioned transversely across the housing 23' with the air chamber 26projected from one side thereof. The housing 23' at the end III,thereof, is formed to extend partially about the periphery of the fins38 to direct the air moved by the fan 42 in a heat exchange'relationtherewith. The fan 42 and driving motor 4I therefor are mounted at theopposite end H2 of the housing, and project the heated air rom thehousing end III. The operation of the heating unit I2 is similar in allrespects to the heating unit I2 of Fig. 3 so that a further descriptionthereof is believed to be unnecessary.

The heating unit I2 is illustrated in Fig. 9 for heating an inflatablegarment I I3 adapted to be worn by the operator of an aircraft. As shownin Fig. 9 the air circulating fan 42 is of a sirocco type, as comparedto the propeller type fan 42 shown in Fig. 3. The sirocco fan operateswith less volume but at a higher pressure than the propeller type fan,which pressure is utilized to inflate the garment H3. The discharge end45 of the heating unit I2 is provided with an extension 4 having aflexible conduit H6 adapted for fluid connection with the garment H3 asby a slot and bayonet connection I I1. On operation of the heating unitI2 the pressure of the heated air as produced by the fan 42' issuflicient to inflate the garment H3 and to circulate heated air thereinand about the body of the operator.

Fluid connected at one end with the extension H4 and at its opposite endwith the fan 42 is a by-pass conduit H8 for feeding unheated air intothe garment H3. The extension H4 has a vent or opening H9 for exhaustingheated air.

12 The exhaust of the heated air and the flow of cool or unheated airinto the connection H6 are concurrently controlled by a common valvemember I2I so that any proportion of heated and cool air can :besupplied within the garment I I3.

As shown in Fig. 9 the operator is in a sitting posture. In order tocirculate air entirely about the operator, the garment at the seatportion is provided with a porous cushion I22 which permits heated airto be circulated therethrough. It is to be understood of course that ifthe operator is normally in some position other than a seating position,such as in a prone position which might be assumed by the operatorcarried in the blister or bulge I23 at the bottom of the fuselage I0(Fig. l) the porous material I22 would then be across the front of thegarment. The end of the sleeves, and the neck portion of the garment II3 may be suitably formed with openings to permit heated air to becirculated within the gloves I24 and about the head of the operator.Since the garment I I3 is generally worn over the shoes of theoperatorheated air is admitted about the feet through the tops of the shoes. Byvirtue of this arrangement heated air is positively directed immediatelyadjacent the body of the operator regardless of the air currentconditions present in the compartmentin which he happens to be located.Instead of the garment I I3 being vented at the sleeves or at the throatit may be made out of a suitable porous material or fabric whichgradually permits the heated air to escape therefrom. It is apparent ofcourse that the flexible conduit I I6 can be connected any where aboutthe garment H3 depending upon the normal movements of the operator so asto offer a minimum of interference to such movements.

From a consideration of the above description and drawings, therefore,it is seen that the invention provides a'heating system for furnishingheated air to a plurality of remotely located spaces in which a heatingunit in each of such spaces are operatively connected with common power,air and fuel supply means adapted to be installed in a, minimum ofspace. The air and fuel are supplied separately to each heating unit andare mixed at the unit for burning. The combustible mixture supplied toeach combustion portion for burning is thus retained substantiallyuniform so that each heating unit operates with maximum efficiency.Although air and fuel are separately supplied to all of the heatingunits from common supply sources such air and fuel are in an unheatedcondition so that the problem of heat transmission losses between thevarious heating units is completely eliminated. It is understood ofcourse that the air and fuel connections of a heating unit with acorresponding common transmission line may be of a flexible constructionso that a. heating unit can be readily moved about within acorresponding space or compartment which is to be heated. Further theoperation of the heating system is not dependent upon any air velocitiesresulting from the plane being in flight, and can be operated at alltimes and at all altitudes.

Although the heating system has been illustrated and described inconjunction with an aircraft it is to be understood that the heatingunits may be arranged in any large open space to distribute heated airtherein, or applied to any condition requiring a plurality of heated airoutlets. It is to be understood also that although the invention hasbeen described with respect to several preferred embodiments thereof itis not to be so limited since modifications and alterations can be madetherein which are within the full intended scope of this invention asdefined by the appended claims.

Iclaim:

i. In an air heating system for an aircraft having a plurality of spacestherein, a heating unit in each of said spaces, means separatelysupplying combustion air to said units from a common source, meansseparately supplying fuel to said heating units from a common source,means included in each heating unit for mixing the air and fuel suppliedthereto for burning, and altitude responsive means common to saidheating units and operatively associated with said air supply and fuelsupply means to maintain substantially uniform the air and fuel mixturesupplied to each heating unit over a wide range of altitudes of varyingoxygen contents and pressures.

2. In an -air heating system for an aircraft adapted for operation overa wide range of altitudes of varying barometric pressures andcorresponding oxygen contents, a plurality of heating units, meansseparately supplying combustion air to said heating units includingcommon air moving means, means separately supplying fuel to said heatingunits from a common source, means including means common to said heatingunits and responsive to barometric pressures for controlling the rate offlow of air to said heating units by said air moving means, and meansfor maintaining the rate of fuel feed to each heating unit substantiallyuniform over said range of altitudes.

3. In an air heating system for an aircraft adapted to be operated overa wide range of altitudes having varying atmospheric pressures andcorresponding variations in oxygen content, a plurality of heatingunits, means separately feeding air to said heating units, means commonto said units and responsive to "atmospheric pressures for controllingthe rate of feed of said air to each heating unit, means separatelyfeeding fuel to said heating units from a common source, and pressureresponsive means for maintaining the rate of fuel feed to each heatingunit substantially uniform over said range of altitudes.

4. In heating apparatus utilizing a liquid fuel, the means for supplyingliquid fuel to said apparatus including in combination a supply line,fuel feed means connected in said supply line and having a liquidreservoir therein, expansible means fluid connected with said reservoirand having an air pocket therein, said expansible means being acted uponby the liquid pressures in said reservoir, a sealed enclosure about saidexpansible means having an air pressure therein of fixed value, andmeans in said supply line retarding the flow of fuel from said reservoirtd control the rate of liquid fuel flow to said apparatus.

5. In heater apparatus having means defining a combustion chamber, thecombination of a fuel supply for said combustion chamber including afuel line, fuel feed means connected in said fuel line including a fuelreservoir having an outlet, expansible means fluid connected with saidreservoir and having an air pocket therein, said expansible means beingacted upon by the pressure of the fuel in said reservoir, a sealedenclosure about said expansible means ,having an air pressure therein offixed value, and a longitudinally extending core member arranged withinsaid fuel line at said outlet to retard and control the flow of fuelfrom said reservoir to said combustion portion.

6. In heater apparatus having means defining a combustion chamber, thecombination of a, fuel supply including a supply line fluid connectedwith fuel moving means which produces a pulmeans being expanded by thefluid within acting against the air pressure on the outside thereof, anda sealed enclosure about said diaphragm means having an air pressuretherein of fixed value. said diaphragm means being responsive inoperation to the fuel pulsations in said reservoir to maintain asubstantially uniform fuel pressure at said outlet.

7. In heater apparatus for an aircraft including means defining acombustion chamber, the combination of a fuel supply providing for a,substantially uniform fuel feed to said combustion chamber over a rangeof altitudes of varying atmospheric pressures including a fuel line,fuel feed means connected in said fuel line having a fuel reservoir withan outlet, diaphragm means fluid connected with said reservoir having anair pocket therein, said diaphragm means being expanded by the pressureof the fluid therein acting against the air pressure on the outsidethereof, a sealed enclosure about said diaphragm means having an airpressure therein of fixed value, and a longitudinally extending coremember in said fuel line at said outlet retarding the flow of fueltherethrough to control the supply of fuel to said combustion portion.

8. Aircraft heating apparatus including in combination a plurality ofheating units spaced apart in said aircraft and each having a heatexchanger part, fuel supply means common to all said units, air supplymeans common to said units and means for conducting air therefrom formixing with the fuel for burning, means responsive to altitude changesacting on said air supply means to provide a relative increase in thevolume of air delivered to said heating units as an increase is requiredfor the desired burning of the fuel at increased altitudes, and meansfor conducting heated air away from each heat exchanger part.

9. Apparatus for heating an aircraft, comprising a plurality of fuelburning devices located at different points about said aircraft, a fuelfeed system for supplying fuel to said devices and including partscommon to said devices, an air supply system for supplying combustionair to said devices and also including parts common to said devices, andmeans common to said devices for controlling certain of the common partsof said systems in order automatically to vary the amount of fuel andthe volume of air supplied to each of said devices in accordance withvariations in the altitude at which said apparatus is operated.

'10. In an air heating system for an aircraft, a plurality of fuelburning devices located at different points about said aircraft, aconduit system for supplying combustion air to said devices andincluding a conduit common to said devices and having an air inletopening, damper means for variably opening and closing said opening, aliquid fuel feed system for delivering liquid fuel to said devices andincluding a fuel feed control valve common to said devices, and analtitude responsive device for operating said damper means and saidvalve to maintain substantially {miform the air and fuel mixturesupplied to each of said devices over a wide range of altitudes.

HARRY B. HOLTHOUSE.

REFERENCES CITED The following,v references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Goerg Oct. 17, 1939 Cracker Apr.18, 1899 Batter Feb. 16, 1909 Ofeldt Nov, 2.4, 1908 15 McCollum Apr. 28,1942 Number

